Ocean thermal gradient
The temperature gap between warm surface water and cold deep water.
Natural sources · Solar-derived flows · No. 6
- Natural sources
- Origin: Indirect solar
- Renewable: Yes
In tropical seas, warm surface water sits a kilometre above water near 4 °C, and that gap can run a power plant.
Chart: Illustration: Ocean thermal gradient
Where it comes from
Chart: Map of where it comes from
The tropical Sun heats the top layer of the ocean while water a kilometre down stays near 4 °C; a heat engine runs on the roughly 20 °C gap.
Three things to know
- IRENA counts at least 98 nations and territories with an ocean thermal resource.
- Micronesia's estimated resource is 1,134 TWh a year, far more than its small population could use.
- Steep island slopes matter because they put water 1,000 m deep within a short pipe of the shore.
The journey
- 1 Sun-warmed surfaceTropical seas held at 25-30 °C
- 2 Cold deep waterNear 4 °C about a kilometre down
- 3 Long pipesPump warm and cold water to shore
- 4 Heat engineThe temperature gap drives a turbine
- 5 Island powerSteady supply for diesel-dependent islands